In order to facilitate transmission of an encoded bitstream over a constant bitrate channel, a sending device typically needs information on the bitrate which has been applied when encoding said bitstream. Furthermore, information regarding the bitrate of an encoded bitstream may be needed at a multiplexing device which is configured to multiplex a plurality of encoded bitstreams into a joint bitstream. An example for such a multiplexing device is an MPEG-2 Transport Stream multiplexer. Also a decoding device may need information on the bitrate which has been applied when encoding said bitstream.
A (more or less) rough estimate of the applied bitrate may e.g. be estimated from the actual size of received frames of the encoded bitstream. The quality of such an estimate is, however, dependent on the type of bitstream. Possible types of bitstreams are e.g. constant bitrate (CBR), variable bitrate (VBR) or average bitrate (ABR) bitstreams. A CBR bitstream typically does not require the explicit signaling of a bitrate, because the frames of the bitstream usually have a substantially constant size. On the other hand, in case of a VBR bitstream, the momentary bitrate may vary substantially, such that the quality of an estimate of the bitrate based on the frame size is typically relatively low.
An ABR bitstream exhibits a bitrate which is to be achieved “in average” by the bitstream. A multiplexing device and/or a decoding device of the ABR bitstream typically comprise a buffer of a pre-determined size (e.g. of a pre-determined number of frames and/or of a fixed size in bytes), in order to be able to handle momentary variations of the bitrate. Such bitstreams are called to adhere to a “buffer model”. The present document addresses the technical problem of determining the bitrate of such an ABR bitstream in an efficient and precise manner. In this context, it may be desirable to provide an efficient scheme for signaling information regarding the bitrate, notably in order to increase the accuracy of a bitrate estimate and/or in order to reduce the number of bits which are required for encoding the bitrate information.
The described methods may also be applied to other types of bitstreams. By way of example, the described method may be applied to VBR bitstream in order to determine an indicator of a target or average bitrate of the VBR bitstream.